Process parameters for continuous melting-casting and rolling of copper rod

ABSTRACT

A method is described for the continuous production of copper rod in which copper is continuously melted, continuously cast, conditioned and hot-worked into rod form without any intermediate reheating. The essential steps include control of the melt temperature, oxygen content, solidification point, cast billit temperature and hot-rolling temperature.

United States Patent [.72] Inventors Henry Barrow 496 Lake Ave Lancaster, N.Y. [4086; Jack E. Schmidt, ll East Home Road, Bowmansville, N.Y. 14026; Robert E. Frot nson, 27 Dogwood Road. Williamsville,

N.Y. 14221 [Zl] Appl. No. 864,561 [22} Filed Oct. 7, 1969 [45] Patented June29,197l

[54] PROCESS PARAMETEIiS FOR CONTINUOUS MELTING-CASTING AND ROLLING OF COPPER ROI) 5 Claims, No Drawings 52] U5. Cl. 164/76, 2 9/527.6, 29/5277, 164/87 [51] Int. Cl .1 B22c 11/06 I so Field'of Search w13,ss9,430

[56] References Cited UNITED'STATES PATENTS 3,279,000 10/1966 Cofer et a]. 164/87 X Primary Examiner-Robert D. Baldwin Attorneys-F. Shapoe and R, T. Randig PATENTEU JUN29 I97! mmmmlu:%

PlROCESS PARAMETERS FOR CONTINUOUS MELTING- CASTING AND ROLLING OF COPPER ROD BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously producing copper rod of indeterminate length. This end is accomplished by continuously melting copper which is thereafter continuously cast into a continuous casting machine of the rotary wheel type and the cast bar is thereafter conditioned and hot-worked into rod form without any intermediate reheating between the initial melting of the copper and finished production of the copper rod.

2. Description of the Prior Art The practice of continuously casting copper into vertical rotary molds has shown great promise in full-scale development. However there have been two related problems which deter the length-of-run and consequently the overall economies involved in the continuous casting and rolling of copper rod. These difficulties have been predicated upon the fact that intermittent cracking of the cast bar has been observed in the ascast condition or in the as rolled condition. The broken billet usually exhibits an internal void section In addition, without sufficient process parameter controls high maintenance costs have been incurred by reason of the premature cracking of the copper rotary mold.

The solidification of molten copper in chilled rotary molds has been carried out for quite some time as evidenced by the Properzi US. Pat. Nos. 2,659,978; 2,659,949; 2,856,067 and the Cofer et al. U.S. Pat. No. 3,279,000. It has been found however that the product of the rotary mold casting process sometimes exhibits different crack sensitivity characteristics which appear to be related, inter alia, to the temperature of the molten metal and the oxygen content. When proper process controls are maintained with the overall casting process it has been found that mold cracking is materially reduced resulting in overall lowermaintenance costs. In addition, it has also been noted that variations in the quality of the roller copper bar were observed where the temperature of the molten metal and the solidified bar at various locations during the continuous casting and commencement of hot rolling have not been controlled. It was also noted that when the oxygen content varied, the quality of the rolled rod became unpredictable. This variation in oxygen content was found to be a function of the cupola time, with respect to length of time from the startup time, as well as holding furnace atmosphere, and the temperature of the metal just prior to casting.

It has been postulated that the specific amount of hydrogen in the molten metal will vary with oxygen content and with temperature. Consequently it is believed that this could explain the relation between the oxygen content, hydrogen content and the molten metal temperature. This is predicated upon the fact that there is no uncombined hydrogen in solidified copper. Therefore, the amount of the hydrogen solubility of the copper is related to the amount of superheatin the molten copper. Since free hydrogen combines with oxygen in molten copper to form water, and thence steam or a gas as it leaves the pool, it is desirable to find the necessary oxygen to therewith. In conventional wire bar casting there is ample surface area to dispel hydrogen from the molten metal as it solidifies. In continuous casting it is possible to have a molten center covered by a solidified cross section providing no escape for the evolving hydrogen released by solidification.

Consequently in accordance with this invention it is postulated that by providing a higher oxygen level, a suitable opportunity is presented for the hydrogen to combine with the oxygen when the hydrogen is forced out of solution before the metal reaches solidification temperature. Moreover, with lower molten metal temperatures the hydrogen is forced out before it reaches the mold. As a result thereof a sounder billet will be obtained in the continuously cast bar thereby resulting in fewer breaks and giving better uniformity to the quality of SUMMARY OF THE INVENTION The method of the present invention relates to the production of copper rod in which the copper is continuously cast in a chilled rotary mold, conditioned and hot-worked into rod form without any intermediate reheating. The essential steps comprise controlling the temperature of the melt to a temperature within a predetermined range and at the same time adjusting the oxygen content of the melt to a value within a predetermined range. These parameters must be met at the point of the entry of the molten metal into the rotary mold. Thereafter the speed of rotation of the rotary mold is controlled so as to complete solidification of the bar throughout its cross section before the cross section of solidified bar reaches the level of pouring on rotation of the rotary mold and at the same time maintaining the temperature of the cast billet within a set limit. Thereafter the bar is removed from the groove of the rotary mold and conditioned prior to the commencement of hot-working said conditioning being accomplished and the hot-working commenced before the temperature of the bar reaches a predetermined set lower limit.

An object of the present invention is to provide a process for continuously producing a copper rod.

Another object of the present invention is to provide a process for continuously casting and hot-working copper to produce a copper rod of indeterminate length.

A more specific object of the present invention is to provide a process in which various parameters are controlled for continuously casting and working of copper into rod form of predetermined quality.

Other objects will become apparent to those skilled in the art when read in conjunction with the following description and the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT The starting material for use in the continuous casting of copper bar is preferred to be electrolytic copper plate. These copper plates measure about 40 inches by 40 inches and are approximately three-fourths of an inch in thickness. The copper plates in suitable amounts are preferably charged into a cupola such as a shaft-type furnace where they are melted and the molten metal is discharged at the bottom thereof and flows into a tilting holding furnace which acts to control the volume of the molten metal available to the continuous casting machine as well as provide for control of temperature hydrogen and oxygen as will be set forth more fully hereinafter. While other types of furnaces may be employed, the continuous supply of molten copper offered by cupola melting is quite advantageous.

From the holding furnace the molten metal is metered through a trough to a bottom pouring tundish or pot containing a spout that reaches into the casting machine. By controlling the metering pin disposed within the bottom pouring tundish, the molten metal fiow can be metered to the groove of a vertical rotary mold continuous casting machine. It is before this point that the first two parameters must be controlled in order to prevent undue cracking from occurring in the ascast copper bar.

In this respect it has been found that a molten copper temperature within the range of about 2,020 F. and about 2,100" F. and preferably between 2,025" F. and 2,050 F. provide sufficient fluidity and yet maintain the required degree of superheat so that by controlling the oxygen content, a sufficient oxygen supply for the hydrogen contained within the molten copper is assured thereby markedly reducing the crack sensitivity of the as-cast copper bar. The casting temperature is maintained by conventional manual or automatic firing rate methods and any suitable thermocouple can be employed in order to exercise the degree of control necessary to maintain the temperature of the molten copper within the desired limits of between 2,020 F. and about 2,060 F.

ln batch type operations, the molten copper can always be "poled-down to an oxygen content of between about 0.035 percent and 0.045 percent and subsequent oxygen pickup from a launder and pouring tundish will be negligible if normal precautions are observed. However where continuous casting procedures are employed a more dynamic control is needed. it has been found that particular success has been had by continuously melting copper in an Asarco-type melter. This type of melter however produces relatively high oxygen content metal upon startup, that is, an oxygen content of about 0.035 percent to about 0.085 percent, but within a short time, the metal so provided attains a low oxygen content usually within the range between about 0.003 percent and about 0.008 percent.

It has been found necessary to modify the oxygen content in order to control its value. This may be accomplished practically by introducing air either from compressed air sources or auxiliary blowers in appropriate amounts either at the launder between the melting and the holding furnaces or at the launder between the holding furnace and the pouring pot or both. Modification of the oxygen content where it is present in an excessive amount has been found to be practical by introducing natural gas in an impinging manner at the process points set forth hereinbefore for decreasing the oxygen value. ideally, molten metal oxygen analysis should be taken frequently or preferably continuously so that the appropriate corrective action can be taken.

It has been found however that the incidents of the crack sensitivity of the cast metal bar has been greatly reduced and in some cases substantially eliminated where the temperature of the molten metal is maintained within the range between 2,020" F. and 2,060 F. and the oxygen content of the melt is controlled to a value between about 0.035 percent by weight and about 0.045 percent by weight at its point of entry into the rotary mold. Where the oxygen content is increased beyond about 0.050 percent an undue one exceeds commercial standards for ET? copper rod. On the other hand while the oxygen content can be decreased to below about 0.03 percent, and successful casting of copper pig or wire bars occurs at an oxygen content below about 0.03 percent, it has been found that the crack sensitivity of the bar produced on a rotary mold, as well as cracking of the rotary mold itself, increases as the oxygen content decreases below a value of about 0.03 percent. Accordingly, it is necessary to maintain the molten copper within the required temperature range with the required hydrogen and oxygen content at its point of entry into the groove of the rotary mold continuous casting machine.

The chilled rotary mold continuous casting machine comprises a substantially large wheel with a groove of predetermined geometry in its rim which is closed by a flat steel belt during part of the wheel rotation between the pouring point and the extraction point. This is more clearly set forth in the Properzi patents identified hereinbefore. A pool of molten copper is established and maintained in the groove and water sprays cool the wheel and the belt as the wheel rotates. The solidified bar is extracted from the groove on the side of the wheel opposite the pouring point. it is at this particular juncture that the next critical parameters must be exercised in conncction with the foregoing parameters in order to optimize billet and rod quality, and reduce the maintenance cost of the chilled rotary casting wheel as well as provide for freedom from crack sensitivity as the as-cast bar.

This is accomplished by controlling the speed of rotation of the rotary mold to complete solidification of the cast bar before the solidified bar reaches the level of pouring of the molten metal. in this respect it should be noted that if the cast bar has not solidified completely a molten metal head is formed which, because of the static head provided thereby cause the molten metal to flow back towards the point of the introduction of the molten metal into the rotary groove of the continuous casting wheel. This results in the formation ofa void in the center of the later solidified bar with the result that the cast bar may rupture during subsequent processing. On the other hand, if the heat from the molten metal is extracted at too high a rate, that is, if the speed of rotation of the mold is so slow that the bar solidifies at some distance before reaching its point of extraction from the rotary casting wheel, the temperature will have dropped sufficiently at the commencement of rolling that cold rolling will take place, and the cracked sensitivity of the metal will be greatly increased. Accordingly it is desired to maintain the speed of rotation of the rotary mold to complete solidification of the cast bar before the point that it reaches the level of the pouring spout. ln practice it has been found that excellent results are obtained in a o-foot-diamcter wheel which is rotated at a speed of about 2 revolutions per minute.

in addition, it has been found that another control parameter must be exercised which parameter is the temperature of the cast billet at the point of extraction of the bar. It has been found that the temperature of the bar must be maintained within the range between about 1,700 F. and about 1,800 F. and preferably in the range between l,725 F. and l,775 F. Maintaining the continuously cast bar within this temperature range has been effective for greatly reducing the amount of maintenance costs resulting from premature cracking of the rotary casting mold. Moreover, by maintaining temperature of the bar within the foregoing limits at the point where the continuously cast bar is extracted from the mold appears to aid in assuring the solidification of the bar at the proper height thereby minimizing the tendency to create any internal voids due to improper solidification rate.

in this respect it should be noted that the speed of rotation of the rotary casting mold should be adjusted so that at least the minimum temperature of l,'/00 F. is maintained as the bar leaves the rotary mold. Thus if the bar is below a temperature of 1,700 F. it is necessary to increase the speed of rotation of the rotary mold so that a minimum temperature of about 1,700 F. is attained. On the other hand if the speed of rotation is such that the bar is at a temperature in excess of about 1,800 F. the bar may break because of reduced hot strength. in any event it has been found that the crack sen sitivity of the as-cast bar is greatly reduced where the temperature of the as-cast bar is maintained within the range between about l,700 F. and about l,800 F. prior to the commencement of conditioning of the bar.

Thereafter the bar may be conditioned by chamfering and supplying suitable radii to the upper corners of the bar and by conditioning the surface of the bar completely prior to the commencement of hot rolling. After the cast bar is removed from the rotary casting wheel and traverses the conditioning operation it is fed into a hot-rolling mill. it has been found that the temperature of the bar must be maintained within the range between about 1,600 F. and about l,650 F. and preferably within a temperature range of between about l,600 F. and about l,625 F. By commencing the hot rolling operation at this particular temperature range it has been found that the bar is readily hot-worked without any undue edge checking. Hot working of a bar having a cross-sectional area ranging between about 2.82 square inches to about 5.25 inches into a hot-rolled round having a finished rod size of between about one-fourth and about five-eighths inch in diameter has been accomplished in indeterminate lengths which, when severed had a weight of about 25,000 pounds. 1n winch-diameter rod this corresponds to a length of about 33,000 feet. The control of the temperature of the as-cast and conditioned bar as it enters the hot-working mill must be maintained within the described limits, since if the temperature is substantially higher than about l,650 F. poor dimensional tolerances may be encountered. On the other hand if the bar is too cold upon its entry into the hot mill it has been found that excessive cold working occurs which may result in higher tensile strength values than are desired for hot-rolled rod.

Since the foregoing enumerated process is effective for producing wire rod of indeterminate lengths it will become apparent that substantially heavy coils can be produced by the method of the present invention. in contrast thereto in con- 1 weight or original wire bar can produce about 330 feet of half inch rod. On the other hand by practicing the method of the present invention coils weighing 25,000 pounds can be routinely produced.

in order to more clearly demonstrate the method of the present invention the following schedule of controlled parameters was exercised during a run for producing continuously cast copper rod:

1. Molten copper temperature 2,060 F. prior to introduction into the mold.

2. Oxygen content of the copper before casting-0.040 percent by weight.

3. Speed of rotation of 6-foot-diameter rotary casting wheel 2r.p.m.

4. As-cast bar temperature, 1 ,725 F.

5. Temperature of bar at introduction to the mil- 1 ,610" F.

By maintaining the foregoing parameters various physical and mechanical properties were measured of the material produced by the method of the present invention and compared with the same properties of conventional wire bar batch-type castings which are scalped and thereafter reheated and hot-rolled to the same finish rod thickness.

From table 1 it is seen that the density, grain size, conductivity, tensile strength and elongation of material produced by employing the method of the present invention are at least as good, and in most cases better, than conventional wire bar casting wherein the wire bars are scalped, reheated and thereafter hot-rolled to short lengths as opposed to the process of the present invention which is applicable to the manufacture of indeterminate lengths of continuously cast and continuously rolled copper rod.

We claim as our invention:

1. in the method of producing copper rod in which the copper is melted, continuously east in a rot mold, conditioned and hot-worked into rod form without any intermediate reheating, the improvement of steps comprising, controlling the temperature of the melt to a temperature within the range between 2,020" F. and 2,060 F. and adjusting the oxygen content of the melt to a value of between about 0.030 percent by weight and 0.045 percent by weight at its entry into the rotary mold, controlling the speed of rotation of the rotary mold to complete solidification of the cast bar before the solidified bar reaches the level of pouring while maintaining the temperature of the solidified bar between about 1,700 F. and about l,800 F. at the place of removal of the cast bar from the rotary mold and commencing the hot working of the bar when the temperature of the bar is within the range of about l,600 F. and about l,650 F.

2. The method of claim 1 in which the continuously cast bar is conditioned prior to the commencement of hot working.

3. The method of claim 1 in which the temperature of the as-cast bar at its point of removal from the rotary mold is maintained within the range between about 1,700 F. and

about l,750 F.

4. The method of claim 1 in which the oxygen content is maintained within the range between 0.035 percent and 0.040 percent by weight.

5. in the method of producing copper rod in which the copper is continuously melted, continuously cast in a rotary mold, conditioned and hot-worked into rod form without any intennediate reheating, the improvement of steps comprising, controlling thetemperature of the molten copper at its point of entry into the rotary mold continuous casting machine to a temperature within the range between about 2,025 F. and about 2,050" F. while also maintaining the oxygen content of the molten metal to a value within the range between about 0.035 percent and about 0.040 percent by weight, controlling the speed of rotation mold to complete solidification of the cast bar before the bar reaches the pouring level of the molten metal while maintaining the temperature of the solidified bar within the range between about l,700 F. and 1,750 F. at the point of release of the solidified bar from the rotary mold, conditioning the bar and commencing hot working the bar without any intermediate reheating when the bar is at a temperature within the range between l,600 F. and about l,625 F.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 589 ,30 Dated June 29 1971 n fl menrv Barrow, Jack E. Schmidt. and Robert E. Fromson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Delete drawing accompanying patent.

Signed and sealed this 2nd day of May 1972.

(SEAL) Attest:

EDWARD M.FLEI'CHER, JR. BERT GOTTSCHALK Attesting Officer Co missionerof Patents FORM PO-IOEO 110-69! USCOMM-DC 60378-P6D n u s. ecvenumzm Pmm'ms OFFICE: 1909 D3653!4 

2. The method of claim 1 in which the continuously cast bar is conditioned prior to the commencement of hot working.
 3. The method of claim 1 in which the temperature of the as-cast bar at its point of removal from the rotary mold is maintained within the range between about 1,700* F. and about 1,750* F.
 4. The method of claim 1 in which the oxygen content is maintained within the range between 0.035 percent and 0.040 percent by weight.
 5. In the method of producing copper rod in which the copper is continuously melted, continuously cast in a rotary mold, conditioned and hot-worked into rod form without any intermediate reheating, the improvement of steps comprising, controlling the temperature of the molten copper at its point of entry into the rotary mold continuous casting machine to a temperature within the range between about 2,025* F. and about 2,050* F. while also maintaining the oxygen content of the molten metal to a value within the range between about 0.035 percent and about 0.040 percent by weight, controlling the speed of rotation mold to complete solidification of the cast bar before the bar reaches the pouring level of the molten metal while maintaining the temperature of the solidified bar within the range between about 1,700* F. and 1,750* F. at the point of release of the solidified bar from the rotary mold, conditioning the bar and commencing hot working the bar without any intermediate reheating when the bar is at a temperature within the range between 1,600* F. and about 1,625* F. 